Engines with roller valve lifters require a valve lifter guide to maintain alignment between the roller of the valve lifter and an associated camshaft. For cost and assembly considerations, lifter guides are typically designed to accommodate multiple valve lifters on a common bank of cylinders. These guides are manufactured having straight-edged guide openings that engage flats on opposite sides of the lifters. With metal guides, the spacing of the opening edges is slightly larger than the valve lifter flats to avoid binding. However, tolerance variations can result in excessive clearance between the valve lifter and the metal guide, allowing a higher degree of valve lifter oscillation than desired.
One solution is to use valve lifter guides made of fully composite material to have a tight initial fit on the valve lifter flats. The composite guides take a “set” during engine break in which then results in good alignment without excessive friction load. This compliance and “set” in the composite lifter guide is predetermined and calibrated by the selection of constituents used to make up and process the composite material.
In some engines that use cylinder-deactivation with switching valve lifters, fully composite valve lifter guides are impractical due, for example, to space limitations in the engines and high initial drag. In this case, metal construction valve lifter guides are the only practical choice.